1. Field of the Invention
The present invention relates to a lighting control device of a lighting device for a vehicle and, more particularly, to a lighting control device of a lighting device for a vehicle which controls a lighting operation of a semiconductor light source formed by a semiconductor light emitting device.
2. Background Art
Conventionally, there has been known a lighting device for a vehicle which uses, as a light source, a semiconductor light emitting device such as an LED (Light Emitting Diode), and a lighting control device for controlling a lighting operation of the LED is mounted on the lighting device for a vehicle of this type.
There has been known a lighting control device comprising a series regulator connected in series to an LED and serving to carry out a control for causing a specified current to flow to the LED and a switching regulator for controlling an output voltage applied to the LED to be a maximum voltage depending on a control state of the series regulator. Even if a plurality of LEDs are connected in series to or in parallel with the switching regulator, the switching regulator can control the output voltage in such a manner that a specified current flows to each of the LEDs.
In some cases, in which an output of the switching regulator is short-circuited or grounded, however, a load of the switching regulator is increased so that a failure is caused by an excessive power burden. Furthermore, in some cases, in which the output of the switching regulator is opened due to a disconnection, an output voltage is excessively raised in a switching regulator of a flyback type, for example.
Therefore, it has been proposed that an operation of each switching regulator is stopped to protect each of semiconductor light sources (LEDs) upon the assumption that a current of the semiconductor light source (LED) cannot be controlled through the series regulator when an abnormality (an abnormality caused by grounding on a cathode side of the LED) is generated on at least two of the semiconductor light sources (LEDs) (see Patent Document 1).
Moreover, it has been proposed that an operation of a switching regulator is stopped to protect each of semiconductor light sources (LEDs) upon the condition that an output voltage of the switching regulator is normal when an abnormality (an abnormality of an output voltage of a comparison amplifier which is caused by grounding on a cathode side of the LED) is caused by a reduction in a current of any of the semiconductor light sources (LEDs) (see Patent Document 2).
[Patent Document 1] JP-A-2006-103477 Publication (Pages 6 to 7, FIG. 2)
[Patent Document 2] JP-A-2007-22104 Publication (Pages 7 to 11, FIG. 1).